As odd as it may seem, the forelimb posture of quadruepdal dinosaurs is anything but settled. This is due to several reasons, chief among them being that a large amount of articular cartilage encapsulated the ends of the long bones (see here and here, for example). Since this tissue is rarely preserved, determining how the elbows and shoulders of dinosaurs went together, let alone their possible ranges of movement, is difficult to determine at best. This makes determining how the bones were oriented in life difficult to resolve. Regardless of how much cartilage was or was not there, a dinosaur forearm and that of a large, quadrupedal mammal are different. Without going into a long, drawn-out discussion on the subject, suffice it to say that, like other archosaurs, the radius and ulna of most quadrupedal dinosaurs lie parallel to one another. If the forearm was held as a relatively vertical support structure, it is difficult to envision how the hand would be pronated so that it moved in synchrony with the foot. Large mammals accomplish this by significant crossing of the radius over the ulna: this turns the hand palm-side down (pronation) and essentially allows it to work effectively in tandem with the foot to push the animal forwards. In other words, an elephant hand and foot push in the same direction.

In graduate school (mid-to-late 1990s), I noted what I believed were inconsistencies: 1) sauropod trackways show that the manus is often pronated (although not quite as much as mammals and certainly the palm did not face directly backwards); 2) the forearm bones articulated like they do in other archosaurs, like alligators, that cannot assume an upright, columnar forelimb posture with a pronated hand; 3) quadrupedal dinosaur forelimbs were often restored with the radius crossing the ulna to some degree, which cannot occur when you articulate the bones together. In essence, there appeared to be a mismatch between trackways and bone morphology.

It had been well-known that the hands of most sauropods were a vertically-oriented, tubular metacarpus (palm) with stubby fingers and sometimes a large thumb claw, whereas the hind feet were more what you might expect in a big animal: a large foot spread across a fat pad. Why the difference? I began to notice that when the radius was articulated with the ulna, it was cradled on either side by ulnar processes at the elbow. One of these processes was not present in “prosauropods,” theropods (including birds), and crocs. It occurred to me that, perhaps, the radius had shifted internally in the forearm relative to the ulna, and this “new” process (the craniolateral process) evolved to buttress the humerus where the radius once resided ancestrally. If the radius had shifted medially, this would further “drag” the hand into pronation. There was also a lot of cool Evo-Devo stuff going on at the time, and I was absolutely enraptured with the concept of the digital arch that forms the hand in embryos. Since this arch forms from the ulna side and spreads to the radius side, I hypothesized that a shift in radius position internally could bend the hand into a U-shaped structure.

I published on this in the Journal of Vertebrate Paleontology in 2003, and it is one of my most cited papers. It was, to the best of my knowledge at that time, the simplest “solution” to two “problems” — pronation of sauropod hands and their U-shape.

Needless to say, a lot has happened since 2003. Many, many more sauropods and “prosauropods” have been discovered, and other well-known species have been re-described. In my 2003 paper, I predicted that when the earliest sauropods were found, if they had an ulna with a craniolateral process that hugged the radius, they should also have a U-shaped hand. You know what? I was wrong. My first excursion out to South Africa cinched it for me — I got to examine the forelimb of Melanorosaurus, either an almost-sauropod or a basal sauropod. That one animal blew up my hypothesis — it had a craniolateral process on the ulna, but a flattened hand. End of story. Done.

Well, sort of. Adam Yates and I published on the forelimb of Melanorosaurus in 2007, and we drew attention to this issue. We suggested that the radius might still have shifted proximally at the elbow, but that it did not directly and radically effect the hand. We suggested that the U-shaped hand seen in most “classic” sauropods evolved after this shift and may have enhanced pronation by assuming a U-shape. But we definitely stated that the Bonnan (2003) hypothesis linking the possible shift in the radius and the U-shaped hand was falsified. As we stated in the abstract for that paper:

The forelimb morphology of Melanorosaurus suggests that pronation of the manus occurred early in basal sauropods through a change in antebrachial morphology, but that changes to the morphology of the manus followed later in eusauropods, perhaps related to further manus pronation and improved stress absorption in the metacarpus. Thus, we conclude that changes to antebrachial morphology and manus morphology were not temporally linked in sauropods and constitute separate phylogenetic events.

So, to return to Hutson’s paper, I was surprised that he is apparently unaware of the Bonnan and Yates (2007) paper on Melanorosaurus where we clearly say, yes, there probably was no direct link between pronation and U-shaped hands. Again — the hypothesis put forward in Bonnan (2003), based on what was available and known at the time, is falsified, so far as the U-shaped hand and radius-shift are concerned.

I was also surprised that Hutson claims, for example, that I formulated my original hypothesis within a restricted phylogenetic context. At the time, I had dissected and studied bird and reptile forelimbs, and also examined and articulated where possible the forelimbs of “prosauropods” and theropods, and had examined a variety of mammalian forelimbs — keep in mind, this is all before it was feasible to easily digitize and manipulate sauropod dinosaur skeletons. I reference all of these taxa in additional to numerous sauropods in my study. To suggest my hypothesis was developed within a restricted phylogenetic context is specious. Hutson also suggests that I was unaware of the plesiomorphic condition for pronation in tetrapod forelimbs. I will leave that to my readers and to the scientific community to judge.

Throughout the paper, Hutson uses phrases like “Bonnan reasoned …,” “Bonnan relied upon a suggestion …,” and so forth that imply I did not examine material first-hand. I did, and spent many many months and years agonizing over what I had examined, articulated, and dissected.

I could go on, but my point is this. Science proceeds by making hypotheses, testing them, putting that through the process of peer-review, and the allowing the scientific world community to continue to test and modify those hypotheses. As a scientist, you are going to be wrong, and wrong a lot. Over time, new data are going to emerge, new approaches will crop up, and new eyes will look at old bones. You do the best you can with what you have, but you can’t let perfection be the enemy of progress. No paper and no study is perfect — hypotheses will be overturned. If we waited to publish when everything was perfect, nothing would be.

When your hypotheses have been falsified, it is okay to admit that. In 2007, that is precisely what Adam Yates and I did — we said, yep, Bonnan (2003) got some things wrong because we now have better data, and the data don’t agree with that hypothesis anymore. And you know what? That is going to keep happening — scientists evolve past their older papers, and science is self-correcting. If I were still trumpeting from the hills that my Bonnan (2003) article was totally correct and unassailable, the scientific community would be right to castigate me in light of all the new data.

So I think Hutson misses the point. There are statements in his paper such as, “Unfortunately, pronation research has suffered from a lack of awareness that semi-pronated forearm anatomy is plesiomorphic to Archosauria, and indeed all tetrapods.” I know many colleagues who spend an inordinate amount of time carefully collecting and examining data from fossils and living animals. The issue is not one of ignorance or lack of awareness, but one of difficulty — it is damn hard to elucidate evolutionary patterns of forelimb posture because of so many contingencies. I have grown to appreciate these even more as I’ve ventured into collecting kinematic data on live animals. It ain’t easy, and it never will be perfect.

I wish nothing but the best for Hutson and his future studies on what is admittedly an intriguing evolutionary history among the archosaurs. I do hope that he remembers, when his hypotheses are ultimately changed or falsified, that this is the process of science — and that that’s okay.

A short post to let all interested New Jersey parents and their children know that I will be giving a series of free dinosaur presentations at libraries throughout Atlantic County this July, 2014! My presentations consist of fossils, bones, and dinosaur artwork featuring dinosaurs selected by audience members!

Check out the attached PDF link and poster below, and see when I’m coming to a library near you!

The 6th-8th grade was a special time in my development as a budding scientist. No, I would never say Junior High was my favorite time or that I was popular (ha, it is to laugh). However, it was during this time that I began to devour my first “young adult” and adult books on dinosaurs and zoology. Among them were two by Dougal Dixon, Time Exposure and After Man: A Zoology of the Future. I loved the latter book – for those who don’t know, it is the “journal” of scientist from the future Earth 50 million years from now. As a kid, that book was amazing to me, because it linked together evolution, natural selection, and plate tectonics in ways that were inspiring and downright weird. For example, bats that had become terrifying terrestrial carnivores or rabbit descendants taking the place of modern ungulates! It was one of the first books that taught me that evolution was not directed but subject to the vagaries of the environment and the anatomical baggage of past generations. This had been an unexpected Christmas gift from my Aunt Ramona and Uncle Joel — and it has made that kind of lasting impression!

But I had a serious issue as a 13-year-old with Dr. Dixon’s Tyrannosaurus in the other book, Time Exposure. He called it a scavenger! This could not stand. And so, back in the days before internet or e-mails, I typed up a message to him on my mom’s old typewriter informing him of why Tyrannosaurus must, of course, be a top predator. My evidence? Legs built for fast speed, a heavy head with big teeth, and who had ever seen lions taking the kill away from jackals? (I laugh at this last bit now a lot.) My mom (bless her heart) dutifully sent this letter out to a scientist in the UK (postage? $$$) and I waited for a reply.

And a very nice reply did I receive from the desk of a Dougal Dixon a few weeks later. Whereas he disagreed with some of my headstrong assertions about the lifestyle of Tyrannosaurus, he sent a kind and encouraging letter that meant probably more than he will ever know to me and my career. On the rare occasion I have now crossed paths with him at the Society of Vertebrate Paleontology meetings, I have always let him know how much that simple, kind gesture meant to me.

Then this Spring, I was contacted by Highlights Magazine for Children, a magazine I used to get and to which I drew dinosaur pictures for back in the day. They were doing an illustration of the dinosaur I helped to discover and describe, Aardonyx, in, of all things, Dougal Dixon’s Dinosaurs! They showed me a preliminary illustration and the anatomical “bits” they were going to label. I was flattered and a bit emotional, to be quite honest. Here, I was being asked to comment on a dinosaur I helped discover for a page in a kid’s magazine by one of the paleontologists who had encouraged me all those years ago. The circle was complete.

In the past month, the publisher contacted me with the final illustration as it appeared in this summer’s (2013) Highlights for Children Magazine:

Aardonyx in this year’s Highlights for Children Magazine (summer of 2013) – artwork by Robert Squire. Kindly sent by Andy Boyles. Published with permission of Highlights for Children, Inc. Any formatting anomalies are due to converting a PDF to a JPEG — i.e., they’re my fault.

This serves as a reminder to me that the power of being a scientist who studies dinosaurs and other prehistoric life is that our work directly touches and inspires children to think about science and to wonder about the world beyond their own backyards. So this was my belated Christmas gift this year. And a belated post!

Thanks and gratitude go out to Adam Yates for involving me in the research that led to the discovery of Aardonyx, to Celeste Yates for the beautiful preparation of the beast that allowed us to describe it and now Highlights for Children to illustrate it. And of course, thanks and gratitude to Dougal Dixon.

As I recently learned from a fall in which I broke one of my ribs, gravity is an irresistible force.

My poor broken rib.

Gravity’s relentless pull has shaped the evolution of the skeleton in land vertebrates who have had to stand tall or be crushed. Trees have it easy in that they only have to stand and sway (Vogel, 2003) – our skeletons have to resist gravity while on the move (McGowan, 1999; Carter and Beaupré, 2001). If force equals mass times acceleration, then every time you walk, jog, or climb a flight of stairs, you are pummeling your limb skeleton with forces greater than your body weight! But your bones are alive and they adapt to this daily abuse by changing their shapes to best resist those forces. Therefore, paleontologists, like my colleagues and I, are obsessed with bone shape because it is a proxy record of how the limb skeleton adapted to support and move a fossil animal like a dinosaur. Until we recreate living dinosaurs ala Jurassic Park, limb shape is the next best thing to putting a dinosaur or mastodon on a treadmill.

Many dinosaurs were successful in becoming land giants, whereas a comparative handful of land mammals have ever crossed the 1,000 kg mark (Farlow et al., 1995, 2010; Prothero and Schoch, 2002; Prothero, 2013).

The average dinosaur (excluding birds) weighed in at over 1 ton, whereas the average land mammal barely tips the scales at 1 kilogram. (c) 2013 M.F. Bonnan.

Therefore, you might predict to see stark differences in limb skeleton shape between dinosaurs and land mammals … and yet you don’t! In fact, getting big on land as a dinosaur or mammal usually results in stout columnar limb bones which resist weight combined with a decrease in activities like running or jumping (Christiansen, 1997, 2007; Carrano, 2001; Biewener, 2005; Bonnan, 2007). In essence, you get an interesting but ultimately boring pattern that shows us there are only so many solutions to fighting gravity.

Called the sub-articular surface, this zone supports the slippery and pliable articular cartilage that makes movement possible at joints by decreasing friction and absorbing stress. We focused on this region because: 1) its shape should reflect how the bone beneath the cartilage was reacting to stress; and 2) recent work has shown that articular cartilage thickness in dinosaurs and land mammals differs, being very thick (several centimeters in some cases) in the former and very thin (only a few millimeters) in the latter (Graf et al., 1993; Egger et al., 2008; Bonnan et al., 2010; Holliday et al., 2010; Malda et al., 2013).

What we found surprised us. As land mammals become giants, their sub-articular regions become narrow with well-defined surface features. In contrast, becoming a giant sauropod involves an increase in the sub-articular region combined with a subdued, gently convex profile.

Figure 3 from our PLOS ONE paper — On the X-axis, the sub-articular bone region narrows significantly with increasing size, and the shapes of these regions become more convex and/or distinct.

Why this difference? Our results suggest two interrelated relationships. First, sub-articular bone profile and cartilage thickness go hand-in-hand. In living animals, those with thick articular cartilage (alligators and guinea fowl birds in our sample) have expanded sub-articular regions with gentle convexity, whereas those with thin articular cartilage (the living mammals in our sample) retain narrow and increasingly well-defined sub-articular regions. Hence, seeing the narrow and well-developed sub-articular regions in fossil elephants and Paraceratherium show convincingly that they had very thin articular cartilage. In contrast, the expanded and gently convex ends of the limb bones in sauropods appear to be well-correlated with thick articular cartilage.

Second, and more intriguing, these differences suggest different adaptations to becoming a giant constrained by cartilage thickness. In mammals, it has been well-documented that the best way to disperse stress through thin cartilage is to increase the surface contact area (Simon et al., 1973; Egger et al., 2008). In other words, mammals spread the load by narrowing their joints and increasing surface complexity, allowing the bones to articulate closely. As we say in the paper, becoming a giant mammal means developing highly congruent joints. In contrast, becoming a giant sauropod dinosaur involves retaining thick articular cartilage that presumably deforms under pressure. This would go a long way to explaining the expanded sub-articular surfaces we see in sauropods: deforming a thick block of cartilage safely likely requires enough space over which to spread the load.

What does this all have to do with the frequency of gigantism? We speculate that articular cartilage thickness may have a limiting effect on size. If in mammals the best way to spread stress through a joint is by thinning the cartilage and increasing congruence, you are going to get to a point where the joints are as congruent as possible and the cartilage cannot get any thinner. In contrast, retaining thick articular cartilage at large size might have been one factor that contributed to the frequent evolution of so many dinosaur giants. Therefore, our data suggest that the rarity of large land mammals may be due, in part, to their highly congruent limb joints with thin articular cartilage, whereas the success of sauropod dinosaurs as giants may be tied, in part, to their retention of thick articular cartilage.

Figure 7 from our PLOS ONE paper — This figure conveys the essence of our conclusions: as mammals become giants, their joints become ever more congruent with thinning articular cartilage. For dinosaurs, the cartilage remains thick and the joint region expands.

As we say in the article, we in no way intend this to be the last word on dinosaur gigantism or imply that this was the only explanation for their success as land giants. In fact, we hope our work, which was limited to 2-D profiles of the sub-articular surfaces, will be expanded upon using newer, 3-D technology by future researchers (see for example recent work by Tsai and Holliday [2012]). So the next time you take a walk, think about and appreciate how a narrow slice of cartilage helps ensure your bones glide past one another and don’t smack together. I only wish thick, pliable cartilage was in my poor rib, which deformed and snapped under stresses far, far less than those which pummeled the limbs of giant mammals and dinosaurs.

This study would not have been published without the help and perseverance of my co-authors.

Ray Wilhite is a kindred sauropod spirit, and an associate professor of veterinary anatomy at Auburn College who knows far more about alligator anatomy than I can ever hope to amass. His assistance in helping me twice procure, dissect, and prepare alligators from the Louisiana Rockefeller Wildlife Refuge was invaluable. He also introduced me to Ruth Elsey, the goddess of alligators, whom ended up as an author on one of our previous forays into the relationship between cartilage thickness and shape (Bonnan et al., 2010).

Ray comments on our paper: “For most of the history of vertebrate paleontology scientists and explorers focused on finding new fossils and organizing them into meaningful taxonomic groups. Recently, however, many paleontologists have shifted their focus to trying to understand the biology and functional morphology of extinct species. I believe our study has moved the discussion forward regarding the morphological adaptations of sauropods that allowed the to grow to such gigantic proportions. Our study provides a possible clue about why sauropod humeri and femora have expanded ends and large terrestrial mammals do not. The revelation in recent years that there is most likely a significant portion of the articular surface missing in preserved sauropod limb bones is supported by this study. Slowly but surely we are beginning to not just put flesh on the bones, but put the bones on the bones and see what lay between.”

Simon L. Masters was a former graduate student of mine, and his thesis on the ontogeny of the forelimb in Allosaurus was to form the basis of the theropod dinosaur set in our paper. Simon, along with Jim Farlow, previously helped with the writing and analysis of using shape-based statistics for determining sex from the alligator femur (Bonnan et al., 2008). Simon has done well for himself and I’m happy to say he is inspiring a new crop of STEM students as a high school teacher at the all-girls Beaumont School in Cleveland Heights, Ohio.

Adam M. Yates has been an invaluable friend and colleague, and his contribution to this paper allowed us to compile a great deal of morphometric data on “prosauropods.” More specifically, when he, Johann Neveling, and I were working up a different paper on what would become our new dinosaur, Arcusaurus (Yates et al., 2011), I began running morphometric analyses of the distal ends of dinosaur and archosaur humeri because we had only the distal end of that animal’s humerus. That figure never made the final paper but it was my first hint that something interesting was going on in dinosaurs: as I plotted “prosauropod” and sauropod humeri, I could see that there was this trend towards expansion and slight convexity. I wanted to note that in our Arcusaurus paper, but Adam encouraged me to save the data for a later time … and that time is now.

Christine Gardner was one of my many successful undergraduate honors students. While working with me, she measured nearly all of the Afrotherian mammals in our paper for her undergraduate thesis on long bone scaling in these mammals. Her hard work at collecting and analyzing her dataset not only gave her honors in finishing her undergraduate work, but contributed in a substantial way to our paper. She has also journeyed with me out to the field a number of times, and has successfully landed herself in the graduate program at the South Dakota School of Mines.

Christine had this to say about our study: “It was the summer between my junior and senior years when I officially began my undergraduate thesis project. Obviously a new experience for me, I didn’t entirely know what to expect. Little did I know I’d watch my raw data not only yield my honors thesis, but eventually become part of much bigger research which has ended with my name being published. Not many students get to share this privilege before finishing their Master’s thesis.”

Adam Aguiar is one of my new colleagues at the Richard Stockton College of New Jersey who specializes is understanding the molecular-level details of bone and cartilage biology. After the first draft of the paper, he was invaluable at providing insight into thinking about articular cartilage and its responses to shock and stress. This gave the paper a new lease on life, and I doubt we would have been successful on our next submission had it not been for his encouragement and contribution.

Acknowledgments

We thank the many institutions and individuals that provided us with access to specimens for this study. I cannot possibly list all of them here: much of the archosaur data was collected for previous studies (Bonnan, 2004, 2007; Bonnan et al., 2008, 2010) and the heartfelt thanks and appreciation expressed in those references continues more strongly than ever here. For the present study, we wish to thank the following institutions and staff: AMNH: N. B. Simmons and staff (Mammalogy), J. Meng, J. Galkin, and staff (Fossil Mammals); FMNH: W. Stanley and staff (Mammalogy), K. D. Angielczyk, W. Simpson, and staff (Fossil Mammals); UNMH: R. Irmis, M. Getty, and staff; CLQ: M. Leschin; SAM: A. Chinsamy-Turan and staff; BPI: B. Rubidge and staff. We thank Kimberley Schuenman at WIU for collecting data on felids used in this study. Feedback from Gregory S. Paul, Henry Tsai, and Stephen Gatesy at the 2012 Society of Vertebrate Paleontology meeting further improved our manuscript. Discussions with Jason Shulman at the Richard Stockton College of New Jersey on static physics were helpful. Donald Henderson and an anonymous reviewer provided useful comments, critiques, and suggestions on a first draft of this manuscript. We are also indebted to PLOS ONE editor Peter Dodson for shepherding our manuscript through the PLoS system, and his feedback, comments, and suggestions.

We chose to focus on evolutionary lines of mammals and dinosaurs that gave rise to the very largest land species. For mammals, we focused on the placental (eutherian) lines called Afrotheria and Laurasiatheria because elephants and Paraceratherium, the giant rhino relative, descended from these. For dinosaurs, we focused on the Saurischians because the giant, long-necked “brontosaurs” called sauropods were members. We also selected smaller-bodied relatives of these giants in their family trees to examine how similar or different the sub-articular zones of these giants were to their smaller relatives. To analyze shape, we used a computer program called Thin-Plate Splines that tracks and compares landmark coordinates on bones.

Because bony landmarks and sub-articular surfaces were not always anatomically homologous between archosaurs and mammals, we avoided issues of mixing non-homologous areas in our data by running the analyses on these two groups separately.

Why did we use a two-dimensional analysis instead of a three-dimensional analysis? Undoubtedly, three-dimensional shape analysis would have further enhanced our interpretation of sub-articular shape patterns. However, a number of challenges prevented such an approach:

First and most significantly, the data collected in this study span a period of over 10 years during which time cost-effective and portable three-dimensional scanning technologies for acquiring large bone geometries have only recently started to become available. Had we access to these technologies ten years prior, we would have utilized them, as we plan to utilize such approaches in future studies.

Second, our main goal in this study was to quantify whether or not there were significant differences in the scaling patterns of surface morphology between eutherian mammal and saurischian dinosaur long bones, and whether such differences were correlated with known differences in articular cartilage properties. We emphasize that our goal was not to realistically recreate joint surfaces or establish precise measures of joint articulation, nor do we propose how the three-dimensional shape of the subchondral bone is used to reconstruct joint geometry. Our selection of the humerus and femur furthers our goal: these are long bones in which a significant portion of the subarticular surfaces can be reliably captured and interpreted in two dimensions.

Finally, third, two-dimensional data is valuable, comparable to previous studies, and provides a good first-level approximation of scaling patterns. Just as linear morphometrics informed and directed the study of two-dimensional geometric morphometrics (GM) of long bones, so, too, can two-dimensional GM illuminate where future three-dimensional GM studies can make the best impact. Our study is certainly not the last word on long-bone scaling and subarticular patterns in non-avian dinosaurs. Rather, we hope it inspires and provides the basis for research incorporating three-dimensional technologies in years to come.

I am also finishing my dinosaur course here at Stockton, and that means I give my final lecture on “What I hope you have learned from dinosaurs.” It struck me today that this would make an excellent little blog post as well.

One of my grandfathers was fond of asking me, “Why study dinosaurs? What’s the point?” When you are asked that question enough times, you eventually develop a repertoire of answers. I don’t know if these ever satisfied him, but I do hope they satisfy those willing to listen:

There are the Big Picture Reasons:

First off, dinosaurs are just so damn cool. Those who need convincing haven’t been paying much attention to the plethora of amazing discoveries that have continued at an ever-accelerating pace since the late 1800s.

Dinosaurs put our place in the world into perspective – this is not a world meant for us, but one we have had the happy fortune to inherit from previous generations of life.

Dinosaurs are the perfect ambassadors for science – they bring scientific concepts and the nature of science to children and the public like nothing else I know.

While the doctors and veterinarians of the world are busy saving those people and pets you love, the vertebrate paleontologists are in the trenches at the universities and colleges, teaching the next group of practitioners their anatomy. That’s right – most vertebrate paleontologists are excellent anatomists. A certain Larry Witmer comes to mind …

Want to understand why vertebrate anatomy is the way it is? Ask a vertebrate paleontologist – we have to know all that embryology and evolution stuff to inform our research and to blow your mind. =) The bottom line has always been the anatomy is the result of embryology and evolution … who better to teach that we dinosaur-o-philes? And so that I’m being fair – all vertebrate paleontologists are this excellent, not just the dinosaur ones!

Yes, you say, but we’ve heard these platitudes before. You spoke of hope … where is that? If dinosaurs have taught me nothing else, it is an appreciation for human life. As successful as dinosaurs were, their Encephalization Quotient (their EQ, or brain size) was never too generous. We mammals, on the other hand, have had the evolutionary fortune of inheriting a rather different brain with a typically much higher EQ. To be fair, the birdy dinosaurs around us have enlarged brains compared to their predecessors.

Why is EQ size a reason for hope? Well, EQ by itself is not, but it is what we Homo sapiens do with it that is. I am no anthropologist, but speaking in general terms, here are two things one can say about humans that cannot, so far as I know, be applied to other vertebrate animals:

We can both anticipate the future and act on it.

We can use imagination to bring positive things into concrete existence.

For all of their significance and success, the non-avian dinosaurs could not have anticipated their demise, nor could they have done anything to act on it. Apart from ancient aliens imbuing dinosaurs with a sense of imagination (I can imagine a particular channel of history losing all its credibility), these mighty animals could not have brought forth everything from medicine to concepts of social justice. As a species, we are certainly still working on a lot and have a long, long way to go, but have you ever stopped to think of how unbelievably special and unique it is that we can act on knowledge and create our future?

So this holiday season, and throughout the year, I hope you may reflect on the fact that whereas for non-avian dinosaurs history’s lessons were inaccessible, they are very much an open book for us. If we can anticipate what the future will bring, we can act on it. If we decide to put our imagination to good use, we can create positive change in the world.

The non-avian dinosaurs could not learn from their past, but perhaps we can learn from them … and from our own ancestors.

“So have a toast and down the cup, and drink to bones that turn to dust.” — Oingo Boingo (Danny Elfman’s rock band)

In the last two posts, I outlined many of the reasons why birds and dinosaurs have been “estranged” and are now being reunited as members of the same clade: Dinosauria. If you haven’t read these first two posts, check them out:

Enter the past two decades of embryonic science, studies of evo-devo (evolutionary development), and a proliferation of studies combining old-school developmental anatomy with new-school gene studies. It turns out that the digit identities in the hand are not set like permanent blueprints, but develop from the expression of various developmental genes to concentrations of various proteins. Without going into great detail, we now know that the identity that digits assume (that is, whether they become I or V or something else) depends on how much of a concentration of particular proteins these regions of the hand were exposed to during development. Simply put, higher concentrations of certain proteins trigger genes that, when transcribed and translated (i.e., expressed), ultimately create proteins that form digit I, II, III, IV, or V.

Intriguingly, this means that the relative position of a digit in the embryo’s hand and what that digit actually becomes are different. In other words, a digit in position II could become a digit I if the concentration of various proteins and the expression of certain genes are changed. This has been called the Frame-shift Hypothesis. In this case, the “frame” is the region of gene expression that gives digits their identities, whereas the how this gradient moves in the developing hand is the “shift.” What this all means is that just because you develop a digit in your hand where digit II should be doesn’t at all guarantee that it will become digit II. It might become digit I, for example, depending on the frameshift.

So, to conclude my thread, let me say that it is not at all parsimonious at this point in time to separate birds from dinosaurs. That is equivalent to separating you from mammals. It is no longer enough to argue that all the similarities between dinosaurs and birds are due strictly to an amazing amount of convergent evolution. We have unique skeletal features only birds and dinosaurs share, we have dinosaurs that could not possibly fly possessing feathers, and we even have fossil support to explain why bird and dinosaur hands match up after all.

Let’s face it: birds are dinosaurs. I emphasize that I say this in the scientific sense of “certainty.” Although we can’t be 100% certain in science, these data show overwhelmingly that birds are part of the dinosaur family tree. When you realize that there are over 10,000 species of living birds but only 4600 or so species of living mammals, you realize it is still the Age of Dinosaurs after all.

Throughout the 1970s and 1980s, the hypothesis of a dinosaur-bird relationship was revived in part because of re-study of the Archaeopteryx specimens, the discovery of the “raptor” known as Deinonychus, and a new approach to understanding evolutionary relationships called cladistics.

Archaeopteryx and Deinonychus are known and discussed in great detail in many sources. Suffice it to say John Ostrom, among others, began to notice striking skeletal similarities between Archaeopteryx,Deinonychus, and dinosaurs generally. It was eventually recognized that there are a number of special, shared traits that only seem to occur together in birds and dinosaurs, and especially among predatory dinosaurs and birds. I could provide a substantial list, but here are a few, selected key features:

A fully erect stance where the shaft of the femur (thigh bone) is perpendicular to the femoral head. (Incidentally, the femoral head points inwards towards the pelvis, and this allows the femur to be held vertically.)

The ankle is a modified mesotarsal ankle joint. What this means is that the proximal and distal ankle bones form a cylinder-like roller joint between themselves. You can see the upper part of this roller joint at the end of a chicken or turkey drumstick, and you also see it in dinosaurs.

Predatory dinosaurs and birds have specialized, hollow bones.

Predatory dinosaurs and birds have a three-fingered hand, and Archaeopteryx has a clawed, three-fingered hand with deep ligament pits, just like other predatory dinosaurs.

A large majority of predatory dinosaurs are classified as tetanurans, and it has been discovered that the tetanuran predators and birds have a furcula. Despite earlier suggestions to the contrary, many dinosaurs have clavicles and furcula.

Coelurosaurs are predatory dinosaurs with specialized wrist bones that allow the hand to swivel sideways. In other words, the hand doesn’t flex and extend, it rotates sideways towards the ulna. Guess what other group of vertebrates has this specialized wrist? Birds!

Within coelurosaurs are the maniraptorans, the predatory dinosaurs that include Deinonychus and the now universally-knownVelociraptor. These dinosaurs have highly flexible necks, elongate forelimbs, and the ulna is bowed outwards — the only other vertebrates with these features? Birds.

These observations, while powerful on their own, really started to hit home when placed within a scientifically-testable framework called cladistics. In a nutshell, cladistics relies on special, shared traits rather than overall similarities to determine common ancestry. In extremely simplified form, cladistics attempts to do what your family tree does: group everyone together who is related by common ancestry. Yes, we all have an uncle or group of relatives we wish were not part of our family, but our shared genetic traits still show our close relationships.

Cladistic analyses of dinosaurs among the vertebrates revealed what Huxley had hypothesized all those years ago: birds were not just relatives of dinosaurs, they were a branch of the predatory dinosaur family tree! Birds were dinosaurs just like humans are mammals.

But where were the feathered dinosaurs? Until the 1990s, all paleontologists could do is point to the special, shared traits of Archaeopteryx, predatory dinosaurs, and birds and infer that maybe some dinosaurs had feathers. This ambiguity was seized on by opponents of the birds-as-dinosaurs hypothesis to again suggest all the features (and more) that we have listed here were simply due to an amazing amount of convergent evolution.

Enter the Cretaceous Chinese predatory dinosaur discoveries of the 1990s in the Liaoning Province. Unprecedented soft-tissue preservation in these fossils showed what was predicted by cladistics, Archaeopteryx, the suite of features shared between dinosaurs and birds only, and even back to Huxley’s observations: unmistakable dinosaurs with unmistakable feathers*. And not flight feathers, either. Barb-like and downy-like feathers that ran along the lengths of dinosaurs that could not have flown. These animals would have used the feathers for insulation and perhaps display, but many could not have flown. To tick off a few on the list of feathered dinosaurs discovered since the 1990s: